A Study on Visual Secret Display Student: Ming-Chiang Chen Advisors: Dr. Shyong Jian Shyu and Dr. Kun-Mao Chao 1

Outline Introduction The Visual Secret Display Problem The Visual Secret Display Problem for One Secret The Visual Secret Display Problem for Multiple Secrets The Visual Secret Display Problem for Color Secret Conclusions 2

Outline Introduction The Visual Secret Display Problem The Visual Secret Display Problem for One Secret The Visual Secret Display Problem for Multiple Secrets The Visual Secret Display Problem for Color Secret Conclusions 3

Motivation Securing the displayed information against the peeping attack 4

The Display and The Mask The display D The decoding mask M (a transparency) Operation: Superimposition  (e.g. D  M ) 5 The pixels in the display and the mask are corresponding. Yamamoto et al., Optics Letters, 2003

Limited Viewing Zone Restricting the visible space P D ( P M ): The size of the display (the mask) d V ( d M ): The distance between the viewing position (the mask) and the display 6 Yamamoto et al., Optics Letters, 2003

Restricting the visible space d M 1 '  2.5cm, d M 2 '  10cm, and d V  125cm Limited Viewing Zone 7

Outline Introduction The Visual Secret Display Problem The Visual Secret Display Problem for One Secret The Visual Secret Display Problem for Multiple Secrets The Visual Secret Display Problem for Color Secret Conclusions 8

The Visual Secret Display (VSD) Problem 9 Given a display D showing the secret P, alter the display D and determine a mask M such that (1) the secret is recognizable from the superimposition of the display and the mask (e.g. D  M ), but (2) totally unrecognizable from either of the display and the mask.

The Visual Secret Display (VSD) Problem 10 For the secret still image, # Secrets# MasksProblemsOur Proposed Schemes 1 1 The (1, 1)-VSD Problem Optical Engineering, 2009 n The ( n, n )-VSD Problem Optical Engineering, 2009 The ( k, n )-VSD Problem Future Works The VSD Problem for General Access Structures In Preparation for Submission nn The (1, n )-VSD Problem for Multiple Secrets Optical Engineering, n -1 n The VSD Problem for Multiple Secrets Optical Engineering, 2009 sn The VSD Problem for Multiple Secrets with General Access Structures In Preparation for Submission #: The number of

Katoh and Imai, IEICE, 1996 Stacking the masks onto the display tightly Kobara and Imai, ASIACRYPT, 1996 Yamamoto et al., Optics Letters, 2003 The concept of limited viewing zone Yamamoto et al., The gray and color secret, multiple masks, and two respective viewing zones. Visual Secret Sharing proposed by Naor and Shamir in 1995 Related Works 11

Visual Secret Sharing 12 P … Share 1 Share 2 Share n Share 3 Share i Selecting an arbitrary share as the display Setting the others as the masks

Our Approach 13 The display shows secret P Mask The display shows secret P but P is unrecognizable For recognizing the secret from the display, producing the required mask

Recognition of the secret P For each pixel p  P, we append a certain pixel at left or right randomly. d : a block of two pixels 0 : white 1 : black r : 0 or 1 randomly : a complementary color of p Visual Effects on Colors 14 d = P

The Decoding Mask 15 The mask contains the windows 0 and the shades 1. The windows: let the corresponding pixels through The shades: block the corresponding pixels d  m = P d = m = [ ] M E = D Rows: shares Columns: the corresponding pixels

Pixel Expansion/Contrast 16 Pixel Expansion: as small as possible Contrast: as high as possible d  m = P d = m = [ ] M D E = Rows: shares Columns: the corresponding pixels

Outline Introduction The Visual Secret Display Problem The Visual Secret Display Problem for One Secret The Visual Secret Display Problem for Multiple Secrets The Visual Secret Display Problem for Color Secret Conclusions 17

The (1, 1)-VSD Problem 18 Given a secret binary image P, determine one display D and one mask M such that (1) P is recognizable from the superimposition of the display and the mask (e.g. D  M ), and (2) P is unrecognizable from either of M and D. D MD M P D M

The ( n, n )-VSD Problem 19 Given a secret binary image P, determine one display D and n masks M 1, M 2, …, M n such that (1) P is recognizable from D  M 1  M 2  …  M n, (2) P is unrecognizable from other possible superimpositions of M 1, M 2, …, M n and D, and (3) P is unrecognizable from either of M 1, M 2, …, M n and D.

n  2 The ( n, n )-VSD Problem 20 P DM1M1 M2M2 D  M 1 D  M 2 M1M2M1M2 D  M 1  M 2

The VSD Problem for General Access Structures 21  : a specification of access structures lists the qualified subsets of M. Given a secret binary image P and a specification , determine one display D and n masks M  { M 1, M 2, …, M n } such that (1) P is recognizable from the superimposition of D and the subset of M in , (2) P is unrecognizable from other possible superimpositions of M 1, M 2, …, M n and D, and (3) P is unrecognizable from either of M 1, M 2, …, M n and D.

22 n  3;   {{2}, {1, 3}} DM1M1 M2M2 M3M3 M1M2M1M2 M1M3M1M3 M2M2M2M2 M1M2M3M1M2M3 DM1DM1 DM2DM2 DM3DM3 DM1M2DM1M2 DM1M3DM1M3 DM2M3DM2M3 DM1M2M3DM1M2M3

Outline Introduction The Visual Secret Display Problem The Visual Secret Display Problem for One Secret The Visual Secret Display Problem for Multiple Secrets The Visual Secret Display Problem for Color Secret Conclusions 23

The (1, n)-VSD Problem for Multiple Secrets 24 Given n secret binary images P 1, P 2, …, P n, determine one display D and n masks M 1, M 2, …, M n such that (1) P i is recognizable from D  M i, 1  i  n, (2) P i is unrecognizable from other possible superimpositions of M 1, M 2, …, M n and D, and (3) P i is unrecognizable from either of M 1, M 2, …, M n and D.

n  2 The (1, n)-VSD Problem for Multiple Secrets 25 P1P1 DM1M1 M2M2 D  M 1 D  M 2 P2P2

The VSD Problem for Multiple Secrets 26 Given 2 n -1 secret binary images P 1, P 2, …, P 2 n -1, determine one display D and n masks M  { M 1, M 2, …, M n } such that (1) P i is recognizable from the superimposition of D and a combination of elements of M, 1  i  2 n - 1, (2) P i is unrecognizable from other possible superimpositions of M 1, M 2, …, M n and D, and (3) P i is unrecognizable from either of M 1, M 2, …, M n and D.

The VSD Problem for Multiple Secrets 27 n  2 DM1M1 M2M2 D  M 1 D  M 2 D  M 1  M 2

Outline Introduction The Visual Secret Display Problem The Visual Secret Display Problem for One Secret The Visual Secret Display Problem for Multiple Secrets The Visual Secret Display Problem for Color Secret Conclusions 28

Recognition of the secret P For each pixel p  P, we append a complementary pixel at left or right randomly. Visual Effects on Colors 29 P d =

Recognition of the secret P For each pixel p  P, we append other colors in the palette  at left or right randomly. Visual Effects on Colors 30 d =

n  2 The VSD Problem for Color Secret 31 DM1M1 M2M2 D  M 1 D  M 2 D  M 1  M 2

Only the display contains whole secret color information, and the mask has the windows and the shades merely. The VSD Problem for Color Secret 32 DM1M1

Conclusions 33

The Visual Secret Display Problem 34 Fundamental color features to the human visual system # Secrets# MasksProblemsOur Proposed Schemes 1 1 The (1, 1)-VSD Problem Optical Engineering, 2009 n The ( n, n )-VSD Problem Optical Engineering, 2009 The ( k, n )-VSD Problem Future Works The VSD Problem for General Access Structures In Preparation for Submission nn The (1, n )-VSD Problem for Multiple Secrets Optical Engineering, n -1 n The VSD Problem for Multiple Secrets Optical Engineering, 2009 sn The VSD Problem for Multiple Secrets with General Access Structures In Preparation for Submission #: The number of

The ( k, n )-VSD Problem 35 Given a secret binary image P, determine one display D and n masks M 1, M 2, …, M n such that (1) P is recognizable from D  M i 1  M i 2  …  M i q, with q  k, (2) P is unrecognizable from D  M i 1  M i 2  …  M i q, q < k, and (3) P is unrecognizable from either of M 1, M 2, …, M n and D, where 1  i  n.

Optimization on Pixel Expansion/Contrast 36 Pixel Expansion: as small as possible Minimize the pixel expansion Contrast: as high as possible Maximize the contrast By using Integer linear programming P D MD MM D

Thank you for listening 37

38 Matthias Bernt, Kuan-Yu Chen, Ming-Chiang Chen, An-Chiang Chu, Daniel Merkle, Hung-Lung Wang, Kun-Mao Chao, and Martin Middendorf, Finding All Sorting Tandem Duplication Random Loss Operations, Journal of Discrete Algorithms, submitted. Shyong Jian Shyu, Ming-Chiang Chen, and Kun-Mao Chao, Securing Information Display for Multiple Secrets, Optical Engineering, Vol. 48, No. 5, pp , Cheng-Wei Luo, Ming-Chiang Chen, Yi-Ching Chen, Roger W.L. Yang, Hsiao-Fei Liu, and Kun-Mao Chao, Linear-Time Algorithms for the Multiple Gene Duplication Problems, IEEE/ACM Transactions on Computational Biology and Bioinformatics, accepted. Matthias Bernt, Ming-Chiang Chen, Daniel Merkle, Hung-Lung Wang, Kun-Mao Chao, and Martin Middendorf, Finding All Sorting Tandem Duplication Random Loss Operations, Combinatorial Pattern Matching (CPM), pp , Ming-Chiang Chen and Richard Chia-Tung Lee, Sorting by Transpositions Based on the First Increasing Substring Concept, IEEE International Symposium on BioInformatics and BioEngineering (BIBE), pp , Tung-Shou Chen and Ming-Chiang Chen, A New Search Engine for Chinese Document Image Retrieval Based on Chinese Character Segmentation Features, Journal of Computer Processing of Oriental Languages, Special Issue on WAP and WEB, Vol. 15, No. 4, pp , Tung-Shou Chen, Kwang-Fu Li, and Ming-Chiang Chen, Using Segmentation Feature of Characters for Content-Based Retrieval System of Chinese Document Images, Pan-Yellow-Sea International Workshop on Information Technologies for Network Era (PYIWIT), Japan, Publications

Supplements 39

The Display and The Mask The display D The decoding mask M (a transparency) Operation: Superimposition  (e.g. D  M ) 40

The Display and The Mask The display D The decoding mask M (a transparency) Operation: Superimposition  (e.g. D  M ) 41 The pixels in the display and the mask are corresponding.

Pixel Expansion/Contrast 42 Pixel Expansion: as small as possible Contrast: as high as possible d  m = P d = m = [ ] M D E = Rows: shares Columns: the corresponding pixels